MAX1729

ECB and LCD Display Bias Supply with Accurate Output Voltage and Temperature Compensation

High-Accuracy Bias Supply Enables Use of Low-Cost Color ECB LCDs

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Overview

High-Accuracy Reference Voltage (±1%)
±11ppm/°C Output Voltage Drift
On-Chip Temperature Sensor Output
Accurate Voltage and Temperature Provide:
- Consistent ECB Colors
- Consistent LCD Gray-Scale Contrast
+2.7V to +5.5V Input Voltage Range
Output Voltage Range
- +2.5V to +16V in Internal Feedback Mode
- Programmable in External Feedback Mode
Dynamic Control of the Output Voltage
67µA Supply Current
0.4µA Shutdown Current
10-Pin µMAX Package (1.09mm max height)
Evaluation Kit Available (MAX1729EVKIT)

The MAX1729 micropower step-up/step-down DC-DC converter is ideally suited for electrically controlled birefringence (ECB) and liquid-crystal-display (LCD) bias-supply generation. It provides step-up/step-down voltage conversion and reduces output ripple by using a step-up DC-DC converter followed by a linear regulator. This architecture permits a physically smaller inductor than those used in competing SEPIC and flyback topologies. This device features low quiescent current (67µA typical). A logic-controlled shutdown mode further reduces quiescent current to 0.4µA typical.

The MAX1729 features an input that dynamically adjusts the output voltage to control display color or contrast. It offers two feedback modes: internal and external. Internal feedback mode allows output voltages between 2.5V and 16V, and is specifically designed to hold temperature drift to ±11ppm/°C. External feedback mode allows the MAX1729 output voltage range to be tailored for various displays.

An on-chip temperature sensor with a positive temperature coefficient provides compensation for LCD/ECB display temperature characteristics. In internal feedback mode, the buffered temperature sensor output is read and used to adjust the output voltage via a digital control signal. External feedback mode features an additional compensation method in which the temperature output is summed directly into the feedback network to provide first-order negative temperature compensation of the output voltage. The MAX1729 is available in the space-saving 10-pin µMAX package.

Applications